Manually filled and operated snap-ring binders for stacks of similarly apertured sheets have long been known, but those types of binders or holders do not lend themselves to modern machine filling and assembling machinery. It has been proposed to make the binders and sheet securing pins of plastic while still adhering to manual actuation, or partial actuation by machine. In some cases plastic binders have been utilized for permanent binding, or manual opening for sheet addition with difficulty. It is the object of this invention to bind stacks of sheets by automatic machinery by means of binders that can subsequently easily be opened manually for sheet changing or additions and manual re-closing and securement.